Polyvinyl alcohol (PVOH) has long been used as a protective colloid for manufacturing polymer emulsions to stabilize such emulsions and the literature teaches that a stabilizing effective amount, e.g. 2% to 10% of the monomer weight, may be PVOH. The surfactancy and the effectiveness as a protective colloid both increase as the residual acetate content increases. These emulsions generally become more hydrophilic with increasing amounts of PVOH, and the films of such emulsions becomes more readily re-emulsifiable. The salt content is also reported to have a similar effect. Generally, the partially hydrolyzed grades of PVOH are used as colloids. Fully hydrolyzed grades are rarely used in this way. It is also taught that PVOH as a colloid may be incorporated at the beginning of the polymerization or added to the finished polymer solution. PVOH stabilized emulsions contain almost exclusively polyvinyl acetate and if other monomers are used, surfactants may be required.
U.S. Pat. No. 4,605,589 discloses a vinyl-acetate/ethylene copolymer prepared in the presence of a stabilizing amount of ultra low molecular weight PVOH, with a partially hydrolyzed PVOH preferred.
U.S. Pat. No. 3,094,500 discloses adhesives and surface coatings prepared with a vinyl acetate polymer emulsions containing at least 10% of a partially hydrolyzed low molecular weight PVOH and a surfactant.
While these references and other prior art systems disclose various copolymer emulsions prepared in the presence of PVOH they have a variety of drawbacks with respect to developing a nonwoven binder. The use of surfactants is considered to be detrimental to the bound nonwoven product due to its detrimental effect upon water resistance and because surfactants may act as a lubricant at high temperatures and adversely affect elongation resistance.
A number of these systems also are based on the use of N-methylol acrylamide as a crosslinker which release formaldehyde as they cure. The release of formaldehyde is a cause for health, environmental and regulatory concern. Further, these prior art systems generally have used PVOH strictly for its stabilizing effect, while this invention has found that the use of larger amounts of PVOH is effective as part of the crosslinking system.